import java.util.Scanner;
public class Ks {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int score = scan.nextInt();
		if (score > 100 | scoer < 0)
		   System.out.println("100");
		}else if (score >= 80){
		   System.out.println("A");
		}else if (score >= 70){
		   System.out.println("B");
		}else if (score >= 60){
		   System.out.println("C");
		}else if (score >=0){
		   System.out.println("D");
		}else{
			scan.close();

	}
}